Field Trip Guide Book: Petroleum System of East Java Basin
Instructor: Awang H. Satyana
Years: 2015

REGIONAL GEOLOGY

East Java Basin in the southeastern margin of the Sundaland has recorded complicated tectonic, volcanic, stratigraphic, and structural evolution since the formation of the basin in the Eocene time until Quarternary time. The basin started in the middle Eocene time by rifted structures on complicated basement, considered as a response to subduction rollback to the south of East Java due to deccelaration of subduction rate related to far-field stress of India – Eurasia collision in 50 Ma. The basin has gained its tectonic setting as back-arc basin since the Eocene time. Like other sedimentary basins in Western Indonesia, during the Paleogene-Early Neogene the East Java Basin underwent extensional tectonics and structural styles due to rifting and sagging mechanisms. 

STATIGRAPHY


​Generalized stratigraphic correlation of East Java Basin (Ardhana, 1993)
Smyth et al. (2005) subdivided East Java into four east-west trending zones based on the van Bemmelen (1949)’s physiographic zones. The zones are defined by stratigraphy and structure and, from south to north, are as follows.
  • Southern Mountains Zone: an Eocene-Miocene volcanic arc (named here the Southern Mountains Volcanic Arc) built on Mesozoic basement. Deposits include siliciclastic, volcaniclastic, volcanic and carbonate rocks which generally dip uniformly to the south.
  • Present-day volcanic arc: active from the Late Miocene.
  • Kendeng Zone: the main Eocene-Miocene depocentre in East Java contains thick sequences of volcanogenic and pelagic sediments. It is now an east-west trending thrust belt.
  • Rembang Zone: the Eocene-Pliocene sequence includes shelf-edge deposits such as shallow marine clastic sediments and extensive carbonates. This zone contains one major ENE-WSW fault-bounded high (Rembang High) and many east-west orientated folds.
  • OUTCROP 1.1
  • OUTCROP 2.1
  • OUTCROP 2.2
  • OUTCROP 3.1
  • OUTCROP 4.1
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​New excavation museum of Manyarejo, displaying mammalian fossils at their sites.
​Here, in a large barren area a frequent small eruptions of mud can be observed from several eruption centers. This area shows the activity of a mud volcano on the northern margin of the Kendeng Deep, showing the mechanism of overpressuring, mud diapirism, and mud volcanism.
​Quartz sandstones, sandy clay and orbitoidal limestones croppe out at Braholo river side cliff. The outcrop is part of Ngrayong Member of Tawun Fonnation. In Cepu area the quartz sandstone is a reservoir rock. The orbitoidal limestones contain fragmens and well preserved
molluscas and larger foraminifera (Lepidocyclina and cycloclypera).
​Over 30 meters of chalkified, yellowish-colored planktonic foram-rich limestone belonging to the uppermost portion of the Early Pliocene Ledok Formation are exposed at the quarries. 
​Gelam limestone (Early Miocene) of Bawean Island, showing intensive dissolution creting pores. Some limestones were intruded by magmatic intrusion, resulting crystalline limestone (lower left corner, from Usman, 2012).